Action: Use partial retention harvesting instead of clearcutting

Key messages

Three studies (including one replicated, randomized, controlled study) in Canada found that using partial retention harvesting instead of clearcutting decreased the density of young trees.

Background information and definitions

Alternatives to traditional clearcut harvesting have been examined due to a recognized need to protect forests. Partial retention harvesting, i.e. retention of mature trees at harvest, has become commonly employed to maintain stand structural diversity and therefore sustain biodiversity.

Supporting evidence from individual studies

1

A replicated study in 1999-2000 in boreal forest in Alberta, Canada (Frey et al. 2003) found that partial retention harvesting decreased the cover and root-sucker densityof Populus spp. compared with clearcutting. Cover of Populus spp. (clearcutting: 9%; thinning: 3%) and density of Populus spp. root-suckers (stems/ha) (clearcutting: 74,800; thinning: 53,900) were higher in clearcut sites. Data were collected in August 2000 in twenty 2 x 2 m plots in each of three replicates of clearcutting (complete removal) and partial removal (50% of basal area removed) treatment units (10 ha). Treatments were applied during the winter of 1998-1999.

2

A replicated, controlled study in 1999-2007 in boreal mixed wood forest in Alberta, Canada (Gradowski et al. 2010) found that low logging intensity levels decreased young tree density compared with clearcutting. Young tree density for the dominant species trembling aspen Populus tremuloides and balsam poplar Populus balsamifera was higher in clearcutt plots (15,000/ha) than in 50% (7,000) and 75% tree area retention sites (3,000), and higher in 10% (12,000) than in 75% tree retention sites. In 20% retention sites, density was similar to all other retention levels (9,000). Each of five logging intensity levels: clearcutting (0%), 10%, 20%, 50% and 75% of the area retained were applied in nine 10 ha forest compartments. Regeneration of trembling aspen and balsam poplar was assessed using six 2 × 10 m plots in each compartment (total of 270 plots).

3

A replicated, randomized, controlled study in 1994-2005 in temperate coniferous woodland in British Columbia, Canada (Newsome et al. 2010) found that partial-cutting decreased the cover of understory conifers compared with clearcutting at one of two sites. At one site cover of tall (2-10 m) understory conifers was higher in clearcut (12%) than partial-cut plots (3-6%). Cover of other plants was similar between treatments: tall shrubs (clearcut: 19%; partial-cut: 13-15%), short (<2 m) shrubs (clearcut: 39%; partial-cut: 24-28%), short conifers (clearcut: 2%; partial-cut: 4-5%), herbs (clearcut: 37%; partial-cut: 36-41%) and mosses and lichens (clearcut: 6%; partial-cut: 12-22%). At a second site, cover of plant groups was similar between treatments: tall conifers (clearcut: 8%; partial-cut: 6-8%), short conifers (clearcut: 10%; partial-cutt: 10-14%), tall shrubs (clearcut: 12%; partial-cut: 3-4%), short shrubs (clearcut: 41%; partial-cut: 19-28%), herbs (clearcut: 23%; partial-cut: 21-22%) and mosses and lichens (clearcut: 6%; partial-cut: 13-19%). Data were collected in 2004-2005 in 16 subplots (200 m2) within each of four clearcut and eight partial cut (25-50% of basal area retained) treatment plots (1 ha) in each of two sites. Treatments were applied in 1994-1996.

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Effectiveness

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An assessment by independent experts of the harms of this action to the target group of species/habitat, based on the summarized evidence (0% = none, 100% = major undesirable effects). Undesirable effects on other groups of species/habitats are not considered in this score. The harms score is combined with the effectiveness and certainty scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

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An assessment by independent experts of the certainty of the evidence for this action based on the summarized evidence (0% = no evidence, 100% = high quality evidence). How certain can we be that the effectiveness score applies to all targets of the intervention (e.g. all birds for an action in the bird synopsis)? This score is based on the number, quality and coverage (species, habitats, geographical locations) of studies. Actions with high scores are supported by lots of well-designed studies with a broad coverage relative to the scope of the intervention. However, the definition of "lots" and "well-designed" will vary between interventions and synopses depending on the breadth of the subject. The certainty score is combined with the effectiveness and harms scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

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The overall effectiveness category is determined using effectiveness, certainty and harms scores generated by a structured assessment process with multiple rounds of anonymous scoring and commenting (a modified Delphi method). In this assessment, independent subject experts (listed for each synopsis) interpret the summarized evidence using standardised instructions. For more details see https://www.conservationevidence.com/content/page/79.